Recently, the requirement for new renewable energy and the interest of the new renewable energy have been more increased due to the serious environmental pollution and the lack of fossil fuel. In this regard, a solar cell is spotlighted as a pollution-free energy source for solving the future energy problem because it rarely causes environmental pollution and has the semi-permanent life span and there exists infinite resources for the solar cell.
Solar cells may be defined as devices for converting light energy into electric energy by using a photovoltaic effect of generating electrons when light is incident onto a P—N junction diode. The solar cell may be classified into a silicon solar cell, a compound semiconductor solar cell mainly including a group I-III-VI compound or a group III-V compound, a dye-sensitized solar cell, and an organic solar cell according to materials constituting the junction diode.
A solar cell made from CIGS (CuInGaSe), which is one of group I-III-VI Chal-copyrite-based compound semiconductors, represents superior light absorption, higher photoelectric conversion efficiency with a thin thickness, and superior electro-optic stability, so the CIGS solar cell is spotlighted as a substitute for a conventional silicon solar cell.
In general, the efficiency of the CIGS solar cell can be improved by diffusing sodium into a light absorbing layer. Meanwhile, according to the CIGS solar cell of the related art, the sodium may not be sufficiently supplied to the light absorbing layer or the supply of the sodium to the light absorbing layer may not be readily controlled.
The minimum unit of the solar cell is called a cell. In general, one cell generates a very small voltage of about 0.5V to about 0.6V. Therefore, a solar cell module, which is fabricated in the form of a panel by connecting a plurality of cells to each other in series on a substrate to generate voltages in a range of several voltages V to several hundreds of voltages V, is used. FIG. 1 is a sectional view showing a solar cell module according to the related art. Referring to FIG. 1, a front electrode layer 60 of a first cell C1 makes contact with a back electrode layer 21 of a second cell C2, so the first cell C1 is connected to the second cell C2. The front electrode layer 60 of the first cell C1 is abruptly bent in the vertical direction and connected to the back electrode layer 21 of the second cell C2. However, if the front electrode layer 60 is bent, it may interfere with the movement of electrons in the front electrode layer 60, so connection resistance between the cells may be increased.
Further, the support substrate has the thermal expansion coefficient different from that of the solar cell, so that the CIGS solar cell module according to the related art is bent through a heat treatment process in the manufacturing process. Accordingly, the solar cell module is delaminated from the support substrate.